This invention relates to a method of explosively bonding at least two metals together without forming interface waves during the bonding process, particularly to an explosive composition of use in the method and, more particularly, to the multi-metallic product thereof.
The present invention relates to a method of producing explosively bonded interfaces of a pair of metals without producing troublesome interface waves. These interface waves are associated with frequent failure, particularly in certain materials, in the form of cracks which emanate from the crests of the waves at an angle of approximately 45xc2x0 to the plane of the interface. A second problem is that the vortex of each resultant wave contains a mixture of the two materials forming the bonded interface. In certain metal combinations, a brittle intermetallic interface is formed which substantially weakens the bond. The presence of waves imposes process limitations as wave amplitude increases as a function of increasing distance from the point of initiation. This ultimately reaches a point where the amplitude forms a relatively substantial proportion of the thickness of, say, the thinner material and failure again occurs in the form of cracks emanating from the wave crests. Turbulent flow of metal occurring during the formation of the waves also results in a high level of work hardening of the metal surface layers at the interface to affect the metal properties in this area. This is an undesirable result in many instances.
By eliminating the waves from the interface, the bond can be strengthened and the source of potential cracking removed. The size and area of clad metal plate which can be produced is no longer limited by the distance from the initiation point at which the onset of wave-ssociated cracking appears. Thus, by removing the interfacial waves to produce a flat interface, many of the current limitations of explosive bonding can be removed to considerably extend bonding capabilities and a superior bond can be achieved.
The interface geometry of any specific metal combination, which includes the shape of any waves produced or the production of a flat interface, is controlled by the angle, known as the collision angle xcex2, at which the two colliding surfaces meet during bonding. This collision angle xcex2 is controlled by the following parameters:
(a) the detonation velocity of the explosive,
(b) the velocity at which the surfaces are propelled towards each other,
(c) the angle at which the two surfaces are initially inclined prior to the detonation of the explosive.
Each of these parameters is included in a bonding arrangement known as the angular geometry. Plain, or flat, interfaces have been produced in the past using this arrangement and these parameters are known to some degree. However, a full determination of their characteristics has not been possible because, when using the angular geometry arrangement, the aforesaid three factors are interdependent and steady state conditions for bonding cannot be implemented. The reasons why conditions are not steady state under the angular geometry arrangement are hereinafter explained.
It is an object of the present invention to provide an improved explosive composition for use in explosive bonding of two metals together which reduces the production of interface waves during the bonding process.
It is a further object of the invention to provide an improved explosive bonding method which reduces or prevents the production of disadvantageous interface waves.
It is a further object to provide a multi-metallic bonded product made by the aforesaid method and which is devoid of interface waves.
Accordingly, in one aspect, the invention provides an improved explosive composition comprising a base explosive in admixture with an inert particulate diluent, the improvement wherein said diluent comprises an inert material having a mean particle size selected from 0.05 mm to 0.1 mm, a hardness value of not less than 4 mohs, and a plurality of faces and edges.
The present invention provides a new form of diluent which can be added in relatively greater proportions than prior art diluents with a base explosive can produce an explosive mixture which can sustain detonation at velocities as low as 1,200 m/sec. Sand or grit, of a particular physical form as herein defined, is such a diluent.
The present invention thus gives a new capability to manufacture explosive mixtures which can produce explosive bonds characterized by having a flat interface which has reduced or is totally devoid of waves and their associated problems.
The particles size of the diluent is a feature which governs the preferred volume and weight of diluent which is added to attain a specifically desired velocity of detonation. The smaller the particle size the less volume or weight of diluent is required. The recommended particle size should, preferably, not be less than 0.05 mm and the maximum particle size should, preferably, not exceed 1 mm. The particle shape and hardness of the diluent are features which affect the sensitivity of the explosive composition and it is most preferred that the particles be both multi-faceted and angular with a hardness value exceeding 4 mohs if the sensitivity of the explosive is to be maintained when the proportion of diluent is sufficiently high to obtain detonation velocities as low as 1,200 m/sec. Provided these requirements are met, the diluent material can take various forms. A preferred diluent is sand or grit in the form of calcium silicate more conventionally used for the sand blasting of surfaces. The characteristics of these materials meet the aforesaid physical requirements of size, shape and hardness to give the desired preferred detonation velocities below 1,800 m/sec and which produce flat, explosively bonded interfaces when bonding by the parallel geometry as hereinafter explained.
Other diluents can be used provided that the diluent material contains an appropriate particle size distribution and the particles are of an equally appropriate shape and hardness. A proportion of particles outside this range can be included with little effect provided that this proportion is not excessive as the uniformity of the explosive performance will be affected as this proportion is increased. The respective proportions of the explosive mixture and the diluent will depend upon the characteristics of the two components. Preferably, the proportion of diluent of the form having the physical characteristics of use in the present invention, normally exceed 40% W/W if detonation velocities below 1,800 m/sec are to be obtained and sustained.
In a further aspect, the invention provides an improved method of explosively bonding a first metal to a second metal with an explosive composition comprising a base explosive in admixture with an inert particulate material, the improvement wherein said composition is as defined hereinbefore.
The method according to the invention is applicable to both explosive bonding wherein the metals are in the parallel relationship and the angular relationship as hereinafter described.
The invention in further aspects provides a method of explosively bonding a first metal to a second metal, the first metal having a first surface and a second surface, the second metal having a third surface, said method comprising (a) locating the first metal adjacent said second metal such that said first surface opposes said third surface; (b)locating an explosive composition adjacent said second surface; and (c) detoning said explosive as to effect displacement of said first metal towards said second metal to bond said first surface to said third surface, the improvement wherein said explosive composition comprises a composition as herein before defined.
Preferably, the first surface is located parallel to the third surface or at an acute angle to the third surface.
The invention composition and method is of particular value with ammonium nitrate containing base explosives, for example, amatol and ANFO.
In a further aspect the invention provides the multi-metallic product of the aforesaid method, which product has relatively low or is devoid of interface waves
The process according to the invention is valuable also in providing multi layered metal products comprising three or more explosivelyxe2x80x94bonded metals together. This is of particular value where two metals having an intervening third layer of a metal interlayered therebetween are explosively bonded according to the process of invention. A preferred example of such a process involves a niobium interlayer between a cladder of titanium and a steel substrate. The resultant trimetallic product is waveless at each of the two interfaces, i.e. at the niobium/steel interface and the niobium/titanium interface.